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With energy efficiencies close to two times higher than traditional photovoltaic (PV), concentrated photovoltaic (CPV) systems represent a promising solution for solar power generation. In the same way, the converging Levelized Cost of Energy (LCOE) of both technologies favors interest toward CPV systems. In order to assess more clearly the potential of this technology, an up-to-date evaluation of the power electronic conversion techniques used in CPV to increase the yielded energy is crucial. This assessment not only sheds light on the latest advancements, but also provides insights into design trade-offs, performance limitations, and potential areas for improvement in CPV systems. This work focuses on the DC/DC converters used as an intermediary stage of conversion between the panels and a central grid-tied inverter. Electrical and economical metrics are used to compare actual converters developed and presented in a comprehensive literature review.

The simplest DC/DC converter for supplying an Internet-of-Things device is definitely a switched-capacitor converter. The voltage from a mere 1.2 V battery may be stepped up to 2 V. A quite large operating frequency is required in order to reach the smallest possible output impedance value of the DC/DC converter. The overall efficiency is then limited even more so if the power area density of the system should be large. The article details how a microbial fuel cell may substitute one capacitor in the switched-capacitor converter, achieving a better efficiency at a much lower operating frequency. In that perspective, the microbial fuel cell acts as a kind of battery range extender. Some limitations exist that are discussed. A simple converter is experimentally evaluated to support the discussion. Substituting a microbial fuel cell inside a 100 μW switched-capacitor converter compensates for losses in the order of 5% of efficiency. Moreover, the microbial fuel cell extends the lifespan of the battery, as 1.6 V output voltage is still possible when the battery voltage drops to 0.8 V. More than 94% efficiency is measured for a range of output power between 100 μW and 1 mW, which is sufficient to address a lot of frugal IoT applications.

This work details the design and experimental characterization of a 2D rectenna for scavenging radio frequency energy at 2.45 GHz (WiFi band), fabricated on polylactic acid polymer (PLA) using a plastronics approach. PLA is the RF substrate of both antenna and rectifier. The two transmission line (TTL) approach is used to characterize the substrate properties to be considered during design. A linearly polarized patch antenna with microstrip transmission feeding is connected to a single series diode rectifier through a T-matching network. The antenna has simulated and measured gain of 7.6 dB and 7.5 dB, respectively. The rectifier has a measured DC output power of 0.96 μW at an optimal load of 2 kΩ under RF input power of −20 dBm at 2.45 GHz. The power conversion efficiency is 9.6% in the latter conditions for a 54 × 36 mm patch antenna of a 1.5 mm thick PLA substrate obtained from additive manufacturing. The power conversion efficiency reaches a value of 28.75% when the input power is −10 dBm at 2.45 GHz. This corresponds to a peak DC power of 28.75 μW when the optimal load is 1.5 kΩ. The results compare significantly with the ones of a similar rectenna circuit manufactured on preferred RF substrate.

Harvesting of ambient radio-frequency energy is largely covered in the literature. The RF energy harvester is considered most of the time as a standalone board. There is an interest to add the RF harvesting function on an already-designed object. Polymer objects are considered here, manufactured through an additive process and the paper focuses on the rapid prototyping of the harvester using a plastronic approach. An array of four antennas is considered for circular polarization with high self-isolation. The RF circuit is obtained using an electroless copper metallization of the surface of a 3D substrate fabricated using stereolithography printing. The RF properties of the polymer resin are not optimal; thus, the interest of this work is to investigate the potential capabilities of such an implementation, particularly in terms of freedom of 3D design and ease of fabrication. The electromagnetic properties of the substrate are characterized over a band of 0.5–2.5 GHz applying the two-transmission-line method. A circular polarization antenna is experimented as a rapid prototyping vehicle and yields a gain of 1.26 dB. A lab-scale prototype of the rectifier and power management unit are experimented with discrete components. The cold start-up circuit accepts a minimum voltage of 180 mV. The main DC/DC converter operates under 1.4 V but is able to compensate losses for an input DC voltage as low as 100 mV (10 μW). The rectifier alone is capable of 3.5% efficiency at −30 dBm input RF power. The global system of circularly polarized antenna, rectifier, and voltage conversion features a global experimental efficiency of 14.7% at an input power of −13.5 dBm. The possible application of such results is discussed.

Ambient radiofrequency (RF) energy scavenging has been recently addressed with a wide range of studies to provide alternative powering for low-power applications. However, due to the low power level of the ambient electromagnetic field, the efficiency of the latter systems is still below expectations. Multipath in the environment may be considered and antenna diversity is then a solution for quasi-omnidirectional RF reception to reach a higher probability of receiving energy in a realistic situation. A 3D flexible antenna diversity, which can be integrated into the rectangular packaging, is proposed in order to take advantage of system packaging form. The angle and polarization diversity antenna was designed on flexible substrate in order to achieve the flexibility and low-cost. This design overcomes the low performance of the substrate while maintaining a compact, high isolation, and good radiation efficiency of the antenna. An indoor experimental setup was carried out to compare different rectenna configurations. The measurement results validate the principle and demonstrate the performance of the 3D flexible diversity system. The probability measurements were carried out under precise conditions in indoor scenarios and the results in comparison with statistic models confirmed the performance of the system in such low power conditions.